The present invention is related to a vehicle-purpose object sensing apparatus equipped with object sensing member operated in such a manner that electromagnetic waves are transmitted from transmission members to a predetermined region, and a distance detecting member detects at least a distance of an object based upon a received result of reception members for receiving electromagnetic waves reflected from the object; and equipped with an abnormal condition judging member for judging an abnormal condition of the object sensing member based upon a reception level of the electromagnetic waves received by the reception member.
In order to judge such an abnormal condition that contamination such as mud, snow, and dust is attached to an object sensing member such as a radar apparatus, and then, a sensitivity of the object sensing member is lowered, a system is known from the below-mentioned patent publication 1. That is, when a reception level of reflection waves from an object is lowered than a measurement switching level, the object sensing member is directed to a direction of a guide rail on a road side, or a direction of a road surface, whereas when a reception level of reflection waves from the guide rail, or the road surface becomes higher than, or equal to a malfunction level, the system judges that the object sensing member is under normal operation, and when a reception level is lower than the malfunction level, the system judges that the object sensing member is under abnormal condition.
Another system is known. That is, while reception levels when an object sensing member senses objects are averaged for a predetermined time, when this averaged level value is larger than, or equal to a threshold value, the system judges that the objects sensing member is under normal condition, whereas when this averaged level value is smaller than the threshold value, the system judges that the object sensing member is under abnormal condition.
[Patent Publication 1]
Japanese Patent No. 3488610
On the other hand, the system described in the above-explained patent publication 1 owns the following problem. That is, while the system performs the abnormal condition judging operation by directing the object sensing member to either the side direction or the lower direction, such an object as a preceding-driven vehicle located in front of the own vehicle cannot be sensed. As a result, the operation of the system using the output of the object sensing member cannot be carried out.
Also, the system for judging the abnormal condition by comparing the temporal average value of the reception levels when the object sensing member senses the object with the threshold value owns the below-mentioned problems.
FIG. 7 indicates a conventional abnormal condition judging method of an object sensing member, if a vehicle is driven in a town area. Since a large number of vehicles and a large number of buildings are sensed by the object sensing member in the town road, if the object sensing member is operated under normal condition and the sensitivity thereof is not lowered, the reception levels become high, and the averaged value thereof for 1 minute becomes larger than, or equal to the threshold value (for instance, −28 dB).
On the other hand, in the case that the sensitivity of the object sensing member is lowered due to malfunction and contamination by attaching thereto mud, snow, and dust, namely under abnormal condition, reception levels are lowered. Then, an averaged value of these reception levels for 1 minute becomes smaller than the threshold value. As a consequence, the system can firmly judge as to whether the sensitivity of the object sensing member is under normal state, or under abnormal state by comparing the averaged value of the reception levels for 1 minute with the threshold value.
However, if the vehicle is driven on a desert road where a traffic amount is small, the conventional abnormal judging method owns the following problem. That is, as shown in FIG. 8, in the desert road where the traffic amount is small, substantially none of preceding-driven vehicles and building is sensed, but such an object as a road sign is occasionally sensed. As a result, such a condition that reception levels are high is produced only within a very short time and in a relative long time interval. As a consequence, an averaged value of these reception levels for 1 minute also becomes a value lower than the threshold value, so that an erroneous judging operation is made that the object sensing member is under abnormal condition.